This invention relates to a direct drive vertical power band saw and more particularly to a light duty woodcutting band saw intended for use in home workshops and the like. However, it will be appreciated by those skilled in the art that the broader aspects of this invention are applicable to other power band saws including larger horsepower band saws such as may be used in commercial applications.
Heretofore, band saws intended for home workshop use typically included a rigid, generally C-shaped frame having a drive wheel journalled on the lower part of the frame and an idler wheel journalled on the upper part of the frame with an endless band saw blade entrained around the drive and idler wheels. As was typical, the drive wheel was driven via a remotely located electric motor by means of a belt and pulley drive. Typically, the band saw was mounted on a workstand and the motor was mounted on the legs of the workstand. The requirement of having to buy a separate electric motor and of having to mount the motor on the legs of the workstand appreciably increased the complexity and cost of the band saw. One advantage enjoyed by prior art band saws utilizing belt and pulley intermediate drives is that the surface or cutting speed of the band saw blade could be readily varied by changing the drive pulleys on the drive wheel and on the output shaft of the motor so as to speed up or slow down the surface speed of the band saw.
It will be appreciated that in conventional home workshops and other environments in which light duty band saws are used, typically only 115 volt, single phase, 60 Hz power is available. Because of the power requirements for light duty woodcutting band saws (e.g., a 1/2 or 1/3 horsepower motor is typically required), it is highly desirable that a conventional induction 4 pole motor be utilized to drive the saw. If 6 or 8 pole motors are used, these motors are inherently more expensive than 4 pole motors and thus the requirement for a 6 or 8 pole motor would considerably increase the cost and complexity of the motor for the band saw.
A 4 pole induction motor energized by single phase, 60 Hz. 115 volt power generally has a speed of about 1,725 rpm. In the prior art vertical band saws utilizing a belt and pulley intermediate drive, the surface speed of the blade may be readily adjusted merely by changing the ratios between the drive and driven pulleys on the belt and pulley drive. However, in designing a direct drive band saw in which the drive wheel is affixed to and is directly driven by the rotor shaft of the motor, it will be appreciated that the drive wheel of the band saw rotates at the speed of the drive motor.
Direct drive band saws are known utilizing two idler wheels and a directly driven drive wheel in which the drive wheel could be of any desired diameter so as to insure that any desired surface speed of the blade may be obtained. However, these three wheel direct drive band saws are expensive.
While in a two wheel direct drive bandsaw it would be a relatively easy matter to reduce the diameter of the drive wheel such that the surface speed of the blade is within its desired cutting speed range, it will be appreciated that it is highly desirable that the throat of the band saw (i.e., generally the distance between the reaches of the blade entrained around the blade wheels) should be as large as practical so that larger work pieces may be cut on the saw. Also, it is desirable to have as big a diameter of wheel as practical so as to reduce bending of the blade as it is repeatedly wrapped around the blade wheels during operation. By having larger diameter blade wheels, the service life of the blade can be increased.
Further, in cutting wood and other materials which tend to form substantial amounts of sawdust or other fine granular chips, the sawdust heretofore has posed a problem for the drive motor of a band saw located below the saw in that the sawdust would be drawn into the cooling air passages of the motor and into the lubrication system for the bearings of the motor. This accumulated sawdust would oftentimes block the flow of cooling air through the motor causing it to overheat and fail, or would act as a wick so as to draw lubricant from the bearing lubrication system thus resulting in premature failure of the motor.